package com.souche.sts.study;

import java.util.concurrent.TimeUnit;
import java.util.concurrent.locks.AbstractQueuedSynchronizer;
import java.util.concurrent.locks.Condition;
import java.util.concurrent.locks.Lock;

/**
 * @description: 自定义独占锁
 *
 * @author: heqiang
 *
 * @create: 2019-09-25 10:16
 **/
public class Mutex implements Lock {

    //静态内部类，自定义同步器
    private static class Sync extends AbstractQueuedSynchronizer {
        private static final long serialVersionUID = -1776271486756692747L;

        //是否处于占用状态
        protected boolean isHeldExclusively() {
            return getState() == 1;
        }

        //当状态为0的时候获取锁
        public boolean tryAcquire(int acquire) {
            if (compareAndSetState(0, 1)) {
                setExclusiveOwnerThread(Thread.currentThread());
                return true;
            }
            return false;
        }

        //释放锁，将状态设置为0
        protected boolean tryRelease(int release) {
            if (getState() == 0) {
                throw new IllegalMonitorStateException();
            }
            setExclusiveOwnerThread(null);
            setState(0);
            return true;
        }
        //返回一个condition,每个condition都包含了一个condition队列
        Condition newCondition(){
            return new ConditionObject();
        }
    }

    private final Sync sync = new Sync();


    @Override
    public void lock() {
        sync.acquire(1);
    }

    @Override
    public void lockInterruptibly() throws InterruptedException {
        sync.acquireInterruptibly(1);
    }

    @Override
    public boolean tryLock() {
        return sync.tryAcquire(1);
    }

    @Override
    public boolean tryLock(long time, TimeUnit unit) throws InterruptedException {
        return sync.tryAcquireNanos(1,unit.toNanos(time));
    }

    @Override
    public void unlock() {
        sync.release(1);
    }

    @Override
    public Condition newCondition() {
        return sync.newCondition();
    }
}
